Although polyamide resin has a good slidability due to its crystallinity, many studies have been carried out already for achieving better sliding characteristic and a solid lubricant such as molybdenum disulfide, graphite or fluorine resin and a liquid lubricant such as various lubricant oil or silicone oil have been investigated as a main improving agent for sliding (Nonpatent Document 1).
With regard to a solid lubricant among those sliding improving agents, it is necessary to compound a large amount of the solid lubricant if a sliding characteristic of the resin inherently having an excellent sliding characteristic such as a polyamide resin is to be further improved. That significantly lowers the tenacity of the polyamide resin used as a base and, as a result, not only evaluation standards for molded part for automobiles such as heat cycle are not met but also expensive solid lubricant is compounded in a large amount whereby that is not preferred from an economical view. On other hand, although a liquid lubricant is able to give a highly effective slidability to the resin such as engineering plastic in a relatively small amount, its miscibility with the resin used as a base is poor in many cases and it often happens that surfaces of the molded product are polluted with the liquid lubricant whereby, in the product where a slidability is improved using the liquid lubricant as such, the use thereof is limited.
It has been in the meanwhile proposed that various kinds of such lubricants are not compounded but a highly viscous polyamide resin where molecular weight of polyamide resin is made significantly high is used whereby the mechanical characteristic is improved and, at the same time, sliding characteristic such as low friction or low abrasion is improved. It has been also mentioned that a low-molecular compound such as higher fatty acid, higher fatty acid ester or higher fatty acid amide compound is added as an improving agent for moldability if necessary (Patent Documents 1 and 2).
However, when a highly viscous polyamide resin is used, although the sliding characteristic of the product is improved, its moldability or particularly that upon injection becomes very bad whereby fluidity in a complicated molded product, a thin molded product or a composite molded product into which metal or the like is inserted becomes bad, the molding becomes difficult and the use is limited. When a low-molecular compound such as higher fatty acid is compounded for improving the moldability, although the moldability becomes somewhat better, mechanical strength of the molded product significantly lowers to an extent of more than the advantages in the moldability whereby that is not preferred.
(Nonpatent Document)
                1. Lecture on Plastics [16], polyamide resin, p. 66-75 Nikkan Kogyo Shimbun, Ltd. (1970)(Patent Documents)        1. Japanese Patent Application Laid-Open (JP-A) No. 2006-56983        2. Japanese Patent Application Laid-Open (JP-A) No. 2006-56984        